An end face light-emitting diode array has heretofore been known as a high-density light-emitting element array which may increase a coupling efficiency to lenses. The basic structure of such end face light-emitting diode arrays is described in “IEEE Trans. Electron Devices, ED-26, 1230 (1979)”, for example. Conventional end face light-emitting diode arrays, however, have problems such that there are difficulties in fabricating them high-density, compact and low-cost, because each of diodes is to be connected to a driving circuit in order to drive the end face light-emitting diode array.
To resolve these problems, the present applicant has already disclosed a self-scanning end face light-emitting element array having a pnpn structure in which a driving circuit and a light-emitting element array are integrated in one chip (see Japanese Patent Publication No. 9-85985). A three-terminal end face light-emitting thyristor which is used as the end face light-emitting element disclosed in this publication is shown in FIGS. 1A and 1B. FIG. 1A shows plan view and FIG. 1B cross-sectional view taken along the X-Y line in FIG. 1A.
The end face light-emitting thyristor comprises an n-type semiconductor layer 12, a p-type semiconductor layer 14, an n-type semiconductor layer 16, and a p-type semiconductor layer 18 formed on an n-type semiconductor substrate 10; an anode electrode 20 formed on the p-type semiconductor 18 so as to make ohmic contact therewith; and a gate electrode 22 formed on the n-type semiconductor layer 16 so as to make ohmic contact therewith. On the entire structure provided is an insulting film (not shown) made of a light-transmitting, insulating material, on which an Al wiring 24 is further provided (see FIG. 1A). The Al wiring 24 is not shown in FIG. 1B for simplifying the figure. In the insulating film opened is a contact hole 26 for electrically connecting the anode electrode 20 to the Al wiring 26. While not shown in FIG. 1B, a cathode electrode is provided on the bottom surface of the substrate 10.
In this conventional end face light-emitting thyristor, light is emitted from an end face 23 of the semiconductor layers 14, 16 both thereof constitute gate layers. As shown by arrows in FIG. 1B, the most of current fed from the anode electrode 20 flows directly downward (this injected current is indicated by I1), and a part of the current flows going round to the gate electrode 22 (this injected current is indicated by I2). Although both of these injected current I1 and I2 contribute to light generation in the semiconductor layers, the light generated by the current I2 cannot contribute to external light emission from the end face 23 since the current I2 generates light in the area apart from the end face 23. As a result, the amount of light emitted from the end face is reduced only by the amount of light not contributed, thus external light emission efficiency is decreased.